1. Field of the Invention
The present invention relates to a measuring apparatus, and more particularly to a measuring apparatus having a water-proof structure.
2. Related Background Art
Measuring apparatus such as a level, a transit or a theodolite has been known. Each of those apparatus has a base and a housing rotatable about a vertical axis on the base. The transit and the theodolite also have a telescope rotatable about a horizontal axis to permit measurement of an angle in a vertical plane.
A first prior art measuring apparatus has a construction as shown in FIG. 8.
Horizontal shafts 103 and 104 are formed on the opposite side of a telescope 102. The horizontal shafts 103 and 104 are rotatably supported by a pair of bearings 105 and 106 which are fixed to a housing 101 of the measuring apparatus. Thus, the telescope 102 has an optical axis thereof (which is normal to a plane of the drawing) rotatably supported to allow alteration in a vertical plane.
A pair of grooves 102c are formed in the telescope 102 along outer peripheries of the horizontal shafts 103 and 104, and a water-proof cover 125 is attached to the housing 101. The water-proof cover 125 is formed in a ring shape to surround the horizontal shafts 103 and 104, and has a projection 125a on an inner peripheral surface. The projection 125a fits into the grooves 102c. The measuring apparatus has gaps a and b to assure stable rotation of the telescope 102. The gap a is formed between the horizontal shaft bearings 105 and 106, and the horizontal shafts 103 and 104, and the gap b is formed between the projection 125a and the groove 102c.
A vertical shaft 113 is fixed to the bottom of the housing 101, a base holder 115 is provided in the base 124, and a bearing 114 is fixed to the base holder 115 to extend upward at a center. Accordingly, the vertical shaft 113 is rotatably supported by the bearing 114.
A water-proof cover 126 is fixed to the base holder 115 at an outer periphery near the center, and a groove 126a is formed in the water-proof cover 126. A projection 101c is formed around an opening at the bottom of the housing 101, and the projection 101c fits into the groove 126a. A gap c is formed between the groove 126a and the projection 101c to assure stable rotation of the housing 101.
In the prior art measuring apparatus, predetermined lengths of the gaps a, b and c are required in order to assure the stable rotation of the rotating mechanisms. Since the gaps are very small, the water-proof and dust-proof effect is not affected by ordinary wind and rain, but it is impossible to prevent the penetration of water and dust during a rain or wind.
A measuring apparatus shown in Japanese Laid-Open Utility Model Application No. 2-97612 is provided with a disk-shaped water-proof member as a water-proof device for a rotating mechanism of a housing of a main unit.
As shown in FIGS. 9 and 10, the measuring apparatus comprises a fixed member 55, a rotating member 52 and a clamping ring 58. The fixed member 55 is a base holder which is fixed to a base 124. The rotating member 52 corresponds to the housing 101 of FIG. 8, and it rotates at the top of the fixed member 55 around the vertical shaft 51. The clamping ring 58 rotatably fits to the fixed member 55, has the same center of rotation as that of the rotating member 52 and is rotatable relative to the fixed member 55. A projection is formed on an outer periphery of the clamping ring 58.
Continuous abutments 52a and 58a are formed on the rotating member 52 and the clamping ring 58 to face each other. A disk-shaped water-proof member 60 is arranged relative to the continuous abutments 52a and 58a so that it abuts against both or secures one of them and abuts against the other.
The disk-shaped water-proof member of the water-proof device described above has an effect of sufficiently protecting an electronic circuit in the housing in spite of a simple plate-like structure. However, there is a risk of creation of a gap between the abutments 52a and 58a, and the water-proof member 60 due to a manufacturing tolerance.